One dinghy is equipped with a radar target so the swimmer will show up on radar screens.

He has to feed himself and does not plan to leave the water until coming ashore in Detroit.

The 49-year-old has made direct crossings of the five Great Lakes.

The holder of a number of world records for endurance swimming, Mr Dreyer said he expected to set a new record for the longest distance swum while towing a ton of bricks - a record that does not currently exist.

Before setting off, he said: "Nobody has ever pulled a ton of bricks any distance. Pretty surprising, right?"

The GPS tracking device also comes equipped with a messaging system which can let his crew know if he is OK, or whether he needs assistance.

Mr Dreyer is trying to raise money and awareness for Habitat for Humanity - an organisation which aims to provide safe and affordable housing all over the world.